Project 1: Time Domian Electron Paramagnetic Resonance Imaging: The validation of oxygen imaging by Time Domain Electron Paramagnetic Resonance Imaging (EPRI) has been validated using phantom samples containing the trityl contrast agents Oxo 63, Oxo 31, and Oxo 71 under defined conditions of oxygen content in the range of 0% oxygen (anoxia) to 21 % oxygen (normoxia). Imaging experiments carried out on these samples showed spectral responses, which were in agreement with the oxygen content. Subsequently, experimental conditions in imaging studies such as the gradient magnitudes, field of view, imaging times and image resolution were studied and optimal conditions were arrived at for in vivo imaging experiments. Studies on live animals such as tumor bearing mice suggest that tumors and normal organs such as kidneys, heart, liver etc accumulate significant levels of the contrast agent and images of the contrast agent distribution provides enough image intensity to extract physiological information. With respect to instrumentation, the scanner has been now provided with capabilities to provide uniform RF excitation using shaped RF pulses with nanosecond time resolution. Additionally, data acquisition system has now been developed to provide capabilities for rapid data acquisition making it now possible to collect three-dimensional images with sub-mm spatial resolution in less than 5 minutes. With these capabilities, in vivo experiments can be carried out with high temporal and spatial resolution. Data analyses procedures to extract spatially co-registered functional information are now being tested so that routine in vivo studies can be performed.